Filter devices of the type described above are state of the art. They are used, for example, in fuel systems for internal combustion engines to protect sensitive components, in particular injection systems, from damage caused by pollutants carried in the fuel, such as dirt particles or water content that is to be separated at the filter element. High standards must be demanded with regards to the reliable functioning of such filter devices because the operation of such systems with a non-operable filter device would lead to significant economic losses due to the malfunctions or damage to injection systems that it would cause.